The present invention relates to fluid pressure actuator assemblies of the type including axially moveable diaphragms, and more particularly, to a method of preloading the actuator, and a preload tool for use therein.
Although the present invention may be utilized advantageously with a number of different diaphragm-type fluid actuators (i.e., those operating on hydraulic fluid, pressurized air, etc.), it is especially advantageous when utilized with a vacuum actuator, and will be described in connection therewith.
Vacuum actuators have a number of commercial uses, one of which is illustrated and described in U.S. Pat. No. 4,844,044, assigned to the assignee of the present invention, and incorporated herein by reference. In the cited patent, which illustrates a Roots-type blower serving as a supercharger for a vehicle engine, a vacuum actuator is utilized to control the rotational position of a bypass valve. The bypass valve is located in a duct which bypasses the supercharger. Therefore, and by way of example only, when there is no vacuum being generated (nearly atmospheric pressure in the vacuum chamber), the diaphragm is spring biased toward a position closing the bypass valve, thus building pressure downstream of the supercharger. When there is a substantial vacuum in the vacuum chamber, the biasing force of the spring is overcome, retracting the diaphragm and control rod, and rotating the valve to an open position. In this condition, the supercharger is "bypassed", i.e., there is relatively low pressure downstream of the supercharger.
In a typical vacuum actuator application of the type set forth in the above-incorporated patent, it is desirable to apply a predetermined preload to the biasing spring and diaphragm prior to connecting the linkage rod to its associated valve member, etc. If no preload were exerted on the biasing spring, the fully extended position of the linkage rod would have to correspond to the normally-closed position of the associated bypass valve. This would clearly be undesirable in view of phenomena such as hysteresis and tolerance stackups.
It has been the conventional practice, in setting the preload of vacuum actuators, to utilize a special tool to hold the diaphragm assembly in the desired position, then connect the linkage rod to the bypass valve, and then finally, remove the tool from the actuator.